Mechanical and structural components such as vehicle suspensions, engine blocks, turbine blades and discs, and support structures for motors, pumps, centrifugal machines and the like are commonly subjected to vibration. When this occurs, these components experience a periodic motion in alternately opposing directions from the position of equilibrium which induces loads that can lead to reduced component life.
In certain engineering systems, for example, those made from plastics, elastomers, or other polymerized materials that inherently have a relatively high damping capacity, the vibrational energy associated with their periodic motion is gradually converted to heat or sound as a result of the internal material damping. Thus the system response, that is, displacement amplitude in its components, gradually decreases, which extends safe and reliable usable operating life.
Conversely, in other engineering material systems having relatively low damping capacity (such as ductile cast iron, aluminum or other cast metals), the decay of vibration amplitude is very slow. As an undesirable consequence, such systems are at a higher risk of failure due to fatigue resulting from cyclic variations of the induced stress. An increase in the damping capacity of a metallic material is highly desired in order to reduce overall vibration and, ultimately, system failure.
There are two general groups of contacts that generate friction damping. The first group includes contact between nominally conforming surfaces that do not have a relative rigid-body motion between the surfaces. This is the case of bolted or riveted joints, braided wire ropes, and gas turbine blades. The second group includes contacting surfaces that also have a relative whole-body motion. This is the case of damper rings in gears (solid inserts in brake rotors and damper rings in a brake rotor) and so-called “beanbag” dampers consisting of granular materials (including a body with a filler and loose-mass damper system in brake rotors).
In the first case, relative motion, sometimes referred to as micromotion, may not reach slip conditions, and friction remains in the “static” range associated with tangential stiffness. In the second case, full slip can develop between the surfaces. In any type of contact, friction damping has a preferred range of contact force (contact pressure) within which it becomes most effective. Below such an optimum range, excess relative motion at the interface develops without significant energy dissipation. Above the optimum range, excess contact pressure limits the development of relative motion for friction to act as an effective damper.
Contact pressure between two surfaces depends on their contact geometry and elastic properties which are known to change with surface temperature and temperature gradients. The operating temperature range for metal parts is very wide (from −40° C. after overnight soaks outside in cold climate areas during winter time up to 500° C., e.g., during an operation near the open sources of heat or inside the engine block). Since unwanted metal part failure due to fatigue might occur during any temperature conditions, the change in friction damper effectiveness with the part temperature should be minimized.
Existing technology for friction dampers for metal parts cannot achieve this goal since current knowledge assumes a constant full slip condition between, for example, a rotor and insert surfaces or between insert and filler surfaces. In reality, the full slip condition between the part and insert surfaces or between insert and filler surfaces may change with a change in the part temperature due to unavoidable thermal distortion of the sliding interface resulting in a change in contact pressure from its desired optimal value. Since even a relatively small distortion of an interface between the solid bodies (i.e., continuous inserts) may result in a significant change in contact pressure between them, the deviation of contact pressure from its optimal value may be very large compromising friction damper effectiveness.
In view of the state of the art, it may be advantageous to provide cast mechanical and structural components with appropriate cast-in components that aid in damping. As in so many areas of manufacturing technology, there is always room for improvement related to friction damping relative to interacting mechanical and structural components.